Giraldo Juan Pablo, Wheeler James K, Huggett Brett A, Holbrook N Michele
Harvard University, Department of Organismic and Evolutionary Biology, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Funct Plant Biol. 2013 Feb;41(1):37-47. doi: 10.1071/FP13033.
We tested the hypothesis that an age-dependent reduction in leaf hydraulic conductance (Kleaf) influences the timing of leaf senescence via limitation of the stomatal aperture on xylem compound delivery to leaves of tomato (Solanum lycopersicum L.), the tropical trees Anacardium excelsum Kunth, Pittoniotis trichantha Griseb, and the temperate trees Acer saccharum Marsh. and Quercus rubra L. The onset of leaf senescence was preceded by a decline in Kleaf in tomato and the tropical trees, but not in the temperate trees. Age-dependent changes in Kleaf in tomato were driven by a reduction in leaf vein density without a proportional increase in the xylem hydraulic supply. A decline in stomatal conductance accompanied Kleaf reduction with age in tomato but not in tropical and temperate tree species. Experimental manipulations that reduce the flow of xylem-transported compounds into leaves with open stomata induced early leaf senescence in tomato and A. excelsum, but not in P. trichantha, A. saccharum and Q. rubra leaves. We propose that in tomato, a reduction in Kleaf limits the delivery of xylem-transported compounds into the leaves, thus making them vulnerable to senescence. In the tropical evergreen tree A. excelsum, xylem-transported compounds may play a role in signalling the timing of senescence but are not under leaf hydraulic regulation; leaf senescence in the deciduous trees A. trichanta, A. saccharum and Q. rubra is not influenced by leaf vascular transport.
叶片水力导度（Kleaf）随年龄增长而降低，会通过限制气孔孔径，影响木质部向番茄（Solanum lycopersicum L.）、热带树木腰果（Anacardium excelsum Kunth）、糙叶匹托尼奥木（Pittoniotis trichantha Griseb）以及温带树木糖枫（Acer saccharum Marsh）和红橡树（Quercus rubra L.）叶片输送化合物的过程，进而影响叶片衰老的时间。在番茄和热带树木中，叶片衰老开始之前Kleaf会下降，但在温带树木中并非如此。番茄中Kleaf随年龄的变化是由叶脉密度降低导致的，而木质部水力供应并未相应增加。在番茄中，气孔导度会随着Kleaf随年龄下降而下降，但在热带和温带树种中并非如此。通过实验操作减少木质部运输的化合物进入有开放气孔的叶片中的流量，会导致番茄和腰果叶片提前衰老，但在糙叶匹托尼奥木、糖枫和红橡树叶片中不会。我们提出，在番茄中，Kleaf降低会限制木质部运输的化合物向叶片的输送，从而使叶片易衰老。在热带常绿树腰果中，木质部运输的化合物可能在衰老时间的信号传导中起作用，但不受叶片水力调节；落叶树糙叶匹托尼奥木、糖枫和红橡树的叶片衰老不受叶片维管运输的影响。
